drm/i915/dsc: convert dsc debugfs entry from output_bpp to input_bpc

Convert dsc debugfs entry from output_bpp to input_bpc. The rationale
is to validate different input bpc across various platforms.

v2: -improved commit message (Jani N)
    -styling fixes (Jani N)

Signed-off-by: Swati Sharma <swati2.sharma@intel.com>
Reviewed-by: Manasi Navare <manasi.d.navare@intel.com>
Acked-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Uma Shankar <uma.shankar@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220902190658.9459-2-swati2.sharma@intel.com